1. Field of the Invention
This invention relates to optical storage systems and media, and more specifically, to an optical storage system incorporating a Fabry-Perot cavity to control illumination characteristics at a media surface.
2. Description of the Related Art
Optical media stores information via physical artifacts or discontinuities on a surface of interest. Digital data may be encoded by a series of pits in a reflective mask attached to a supportive plastic structure such as present-day compact disc (CD) media.
Data is read from the media by measuring the distribution of the field reflected by data-bearing features on the surface of interest. Present-day high resolution optical readers measure diffraction caused by data-bearing surface features by combining light reflected from an artifact on a rotating disc with light that was reflected from an adjacent artifact. A data signal is extracted by determining the distortion of the diffraction field and is detected by sampling one or more points within the field using detectors, thereby detecting the phase within the reflected beam as well as its amplitude.
Measuring phase and amplitude provides an improvement over amplitude-only systems, and using a diffracted field detection system permits detection of data-bearing features having very small height variations. However, the limitation on data density is the spatial resolution limitation set by the size of the focused beam on the surface of interest.
Therefore, it would be desirable to provide a method and apparatus having an enhanced spatial resolution for reading data from standard media by illuminating the media with a narrowed beam. It would further be desirable to provide an improved media having enhanced spatial resolution via a narrowed beam.
The foregoing objectives are achieved in an optical storage method and apparatus having enhanced resolution. A media storage for encoding data includes a first reflective surface having physical artifacts corresponding to encoded data and a second partially reflective surface positioned parallel to the first reflective surface and at a tuned optical distance from the first reflective surface, such that at a predetermined illumination wavelength, a beam transmitted through the second partially reflective surface and illuminating the first reflective surface has a minimum radius spot size at the first reflective surface.
As an alternative preferred embodiment, an optical storage system includes an optical illumination/collection subsystem for producing a beam to illuminate a media storage surface and collect the field reflected by it and a partially reflective surface positioned parallel to the media storage surface between the optical illumination system and the media storage surface at a tuned optical distance from the media storage surface. The positioning of the partially reflective surface produces a beam having a minimum radius spot size at the media storage surface.